Directly heated cathode electrode



P ,1938- K. F. J. KIRSTEN 2,114,536

DIRECTLY HEATED CATHODE ELECTRODE Original Filed June 19, 1934 INVENTOR 1%?7 F1 /f/RJ 75/7 ATTORNEY Patented Apr. 19, 1938 UNITED STATES PATENT OFFICE DIRECTLY HEATED CATHODE ELECTRODE Kurt F. J. Kirsten, Seattle, Wash., assignor to Kirsten Lighting Corporation, a corporation of Washington Application June 19, 1934, Serial No. 731,275 Renewed February 19, 1938 2 Claims. (Cl. 176126) This invention relates to improvements in elecitself near this end of the ribbon where the total trodes for luminous arc lamps and it has referpotential across the gas column is the highest. once more particularly to directly heated cathode The result is an unequal distribution of emission electrodes especially designed for use in connecand ionic bombardment of the ribbon over its sur- 5 tion with luminous arc lamps of tubular form as face. Furthermore, the zig-zag arrangement of 5 now extensively used for signs, displays and the ribbon produces unequal heating thereof due illumination. to the fact that the rate of heat radiation from It is the principal object of this invention to all parts of its surface is not uniform because the provide an electrode in the form of a spirally distance of any point of the ribbon surface to wound, metallic ribbon strip placed axially of the the reflecting shield or to adjacent points of the 1 are and electrically connected so that in use the ribbon varies considerably. For this, and other maximum of the are potential will exist at the reasons, such electrodes have a comparatively point of the ribbon where the arc is the longest, short life. thereby to insure uniform emission over the entire The electrode of the present application emribbon surface. ploys a ribbon and an enclosing, heat reflecting 15 It is a further object of the invention to proshield but is so constructed and arranged that vide an electrode of the above stated character these objectionable features of electrodes of the wherein the spiral ribbon is located coaxially type just described are overcome; and there is within a metallic, cylindrical sleeve serving as a provided a uniformity of potential gradient and heat conserving means whereby the heating of uniformity of emission over the entire area of the 20 the cathode electrode is greatly augmented due to ribbon. the fact that a considerable amount of heat In accomplishing the various objects of the energy is prevented from radiating through the invention, I have provided .theimproved details glass and is conserved for the emission space in of construction, the preferred forms of which are the close vicinity of the cathode ribbon. illustrated in the accompanying drawing, where- 25 Other objects of the invention reside in the dein tails of construction, the combination of parts Fig. 1 is a view of a luminous arc lamp having and mode of operation, as will hereinafter be terminal electrodes constructed in accordance fully described. With the present invention.

Explanatory to the invention, it will here be Fig. 2 is an enlarged, sectional view of one of 30 stated that the present electrode is in the nature e ode in ts longitudinal direction of an improvement upon a common form of Fig. 3 is a cross section on line 3--3 in Fig. 2. directly heated cathode electrode now in use and F g- 4 s a Sectional de 0f the ribbon pconsisting of a metallic ribbon folded in zig-zag Referring more in detail to the drawingform to lie in a plane transversely of the direcl des gnates a Sealed, transparent glass tube 35 tion of the arc and supported at its opposite ends here shown as straight but which may be curved by metal rods or conductors sealed into the end angularly formed in different p and in of the glasstube which serves as the container of w ich tube a suitable as such as n n, r a mixthe rare gas or met llic vapor in hich the ture of rare gases, or metallic vapors is contained.

40 luminous are flows This ribbon, which is coated At its opposite ends the tube has the usual ter- 40 with a metallic oxide, is heated electrically from m al enlargements 2-4 in which the electrodes, a special electrical circuit and the heat generated embodied y the present invention are at by the ribbon is the product of the electrical rethese electrodes at p e e m nals being desi sistane of the ribbpn d th square of th nated in their entireties by reference numerals 3 rent carried by the ribbon. The ribbon is usually d p c y. 45 enclosed in a cylindrical, metallic reflecting Ateach end of the tube are three sealed in rods, shield. The luminous are that is established beor metallic conductors; those at one end being tween the ribbons of two electrodes placed at designated by numerals 4, 5 and 6 while those at opposite ends of the tube is a part of another the other end corresponding thereto are desigelectrical circuit superimposed upon the two cirnated by numerals 4', 5 and 6. The rods 5 and 50 cults which serve to heat the ribbons. 5' are of the greatest extent into the tube and are There are objectionable features in the above centrally located. The rods 6 and 6' are shorter. described form of electrode since there must exist The two rods 5 and 6 at one end of the tube and a fall of potential along the ribbon due to its rods 5 and B at the opposite end serve to mount 5 electrical resistance, and the arc will tend to root the metallic ribbon strips 1 and l.

As seen best in Fig. 2, the ribbon strip is formed in a cylindrical spiral attached at one end to the inner end of rod 5 and attached at its other end to rod 6. In the opposite end 01' the lamp tube, the ribbon I would likewise be attached to rods 5' and 6'.

Enclosing the ribbons I and I, respectively, are metallic, cylindrical shields 8 and 8-supported coaxially about the ribbons and spaced therefrom by the rods 4 and 4'. These shields extend slightly beyond the ends of the ribbons and in use they retain and conserve the heat of the ribbons so as to increase the rate at which the ribbon comes to the temperature necessary for efiective emission.

The lamp, as shown in Fig. 1, has circuit wires 9 and I leading respectively from the rods 6 and 6 to terminals of a switch I! through which connection may be made or opened with circuit mains lit-I3. A stablizing impedance I4 is included in the connection 9.

It is understood that if it is so desired, other circuit connections may be made with the rods and 5 for an auxiliary heater circuit and also connections might be made with the rods 4 and I in order to use the shields 88' in the electrode conditioning operation that takes place prior to use of the lamp.

To give a desired stiffness to the ribbon, it is longitudinally cupped, or formed with -an inwardly depressed trough, as is shown in cross section in Fig. 4. It is of prime importance in electrodes of this character employing a ribbon strip that all parts oi the ribbon be equally spaced from the reflecting shield and each part thereof be also uniformly spaced from the adjacent parts so as to insure uniform heating. Unequal heating results in unequal emission, and since the tendency of the arc is to anchor to the parts of higher temperature, this results in still greater heating of these spots with the ultimate destruction of the ribbon. To insure the ribbon against warping or sagging its cylindrical form must be retained, and this is accomplished in this instance by a transverse curvature of the ribbon strip, as is best illustrated in Fig. 4. This construction gives rigidity to the ribbon both transversely and circumferentially. Thus, by this particular mechanical construction great rigidity, even under conditions of incandescence, is obtained. At the same time the heat intensity from the ribbon is kept constant by reason of maintaining the uniform spaces of all of its elements from the refiecting shield and the practical elimination of mutual reflection between adjacent turns.

It is apparent that since the arc circuit is so connected that the maximum arc potential exists between the far ends of the two ribbons 1-4, and the potential drop of the heating circuit oi spiral I is practically equal and in the same direction as the potential drop oi the are along the surface of the spiral, uniform emission of the entire spiral surface will result. This results in a much longerlife of the cathode.

A further advantage of the spiral filament and its symmetrical arrangement within the heat refleeting shield resides in the fact that this filament can be brought to red heat far more rapidly than otherwise. Consequently, the cathode heating circuit and the arc circuit may be closed simultaneously without the danger of excessive cathode sputtering during the arc kindling period which is considerably shortened by the above construction.

A luminous tube properly equipped with electrodes made according to the above disclosure provides for an instant establishment of an arc updn closing the lamp circuit, thus eliminating the usually required thermostats, relays and auxiliary equipment heretofore considered necessary.

Having thus described my invention, what I claim as new therein and desire to secure by Letters Patent is- I. In a lamp of the character described a cathode comprising a coil formed by a ribbon strip, connected in anelectric circuit and having its convolutions uniformly spaced and edgewise to each other and the strip being inwardly troughed throughout its length for stiffness and rigidity, and a heat conserving shield of cylindrical form enclosing the spiral coaxially thereof.

2. In a lamp of the character disclosed, a cylindrical shield, a cathode formed from a fiat, longitudinally troughed ribbon strip helically wound in a coil coaxially within the shield and spaced therefrom and connected at its opposite ends in an electric circuit; said coil being disposed axially in the direction of the arc path in the lamp and having its convolutions evenly spaced apart and edgewise to each other.

KURT F. J. KIRSTEN. 

